1. Field of the Invention
The invention pertains to printer ribbon spools, or cores, and the spindles for holding them. More particularly, it pertains to a novel configuration of core and spindle that permits quick and easy replacement of used printer ribbons and more accurate control over the printer ribbon during use.
2. Description of the Related Technology
In the field of printer technology, a number of different methods have been developed for applying ink to paper, cards, or other print media in a controlled manner. One of the more common methods is through the use of ink ribbons. A flexible ribbon-shaped substrate is impregnated or coated with an ink that readily adheres to paper or plastic card. Although "ink" is the term commonly used in describing this technology, the substance used for printing is typically not an ink in the popular sense of the word. Porous (e.g., cloth) ribbons are usually impregnated with a dark powder which has just enough liquid or gel content to promote its binding characteristics. Non-porous ribbons are typically coated on one side with a dry paste-like substance. In either case, the substance is usually referred to as "ink", and the ribbons as "ink ribbons". Regardless of its technical accuracy, this terminology is common in the industry and is used in the following descriptions. The terminology and technology of printer inks is known and will not be further described here. At the time of printing, the back side of the ribbon is driven by one or more "hammers", which drive the front side of the ribbon against the paper or plastic card being printed upon. This pressure and/or the temperature of these "hammers" transfers some of the ink from the ribbon to the paper or card, leaving an ink deposit on the paper's or card's surface in the shape of the hammer's impact surface. The surface of this hammer may be in the shape of a particular character (e.g., the letter "A"), or a single dot which is combined with other dots to form a character. In either case, the method of transferring ink from ribbon to paper or card is the same. This technology is also known, and will not be further described here.
Because this process removes ink from the ribbon during printing, the ink content of any given portion of the ribbon will be reduced until that area of the ribbon becomes unsuitable for further printing. The ribbon shape was created specifically to address this problem. By moving the ink ribbon past the printed area, a fresh portion of the ribbon will be ready for printing. By supplying fresh ribbon from a supply spool, and recovering the used ribbon on a takeup spool, several feet of printer ribbon (and fresh ink) can be provided in a comparatively small space. For single-pass ribbons, which are usually associated with high print quality, the ribbon advances from one end to the other and is then replaced. Although this process extends the ribbon's effective life, the entire ribbon will eventually become unusable and must be replaced.
In addition to standard ink ribbons and hammers, various other printer technologies have also been developed, such as Thermal Transfer, Hot Transfer, Die Sublimation Transfer, etc. Although these technologies differ from each other in significant ways, two things they have in common are that they typically involve a controlled transfer of the print substance from a substrate onto the print media, and the act of printing depletes the print substance so that the substrate must periodically be replaced. The use of replaceable ribbons, supply spools, and takeup spools is therefore common in many different types of printers. The term "ribbon", as used herein, is meant to encompass any type of printer technology that employs a flat, linear material wound around a spool.
Since replaceability is a requirement for printer ribbons, most printers that use ribbons mounted on spools are designed so that the spool containing the ribbon can be replaced by the operator. Spools are also called "cores", and ribbon/spool combinations are usually sold as a single item. Typically each spool will be mounted on a spindle for operation, the spindle being generally cylindrical in shape and attached to a motor-operated assembly that accurately controls the rotation of the spool. In most cases, only the takeup spool is controlled, while the supply spool is allowed to rotate freely as ribbon is removed from it by the force exerted on the ribbon by the takeup spool. Alternately, the supply spool may also be controlled to help maintain tension in the ribbon. These aspects of ribbon control are known in the art and are not further described here.
The interface between the spindle and the replaceable spool must meet multiple and sometimes conflicting requirements. Removal of the used spool from the spindle and insertion of a new spool on the spindle should both be capable of being accomplished quickly without tools by a non-technical person with little or no instruction. In addition, the interface between the spindle and a mounted spool should be firm enough to keep the spool accurately controlled during operation. Conventional spindle/spool assemblies attempt to accomplish this in one of two ways.
In the first, a protrusion on the outer surface of the cylindrical spindle fits into a recess in the inner surface of the spool (or vice-versa). For proper insertion, the protrusion and recess must be aligned, which requires that the spool be rotated up to 180 degrees before the spool will slip onto the spindle. Without more, this arrangement does not provide protection against longitudinal slippage of the spool during operation, with the resultant possibility that the ribbon will become misaligned with the print area, or that the spool may even slip off the spindle.
In the second approach, a leaf spring or other spring-loaded assembly on the spindle is used to apply pressure to the spool, thus creating a frictional connection which is subject to slippage, both rotationally and longitudinally. Such slippage can be quite detrimental to the proper operation of the ink ribbon.
These conventional spindle/spool assemblies suffer from a number of operational shortcomings, such as:
1) When a new ribbon is installed, the spool can be installed upside down. This places the ink side of the ribbon against the printhead, which can damage the printhead.
2) The spool and spindle are typically made of multiple parts, which increases manufacturing costs.
3) Some spindles have a large outside diameter, which requires a large inside diameter on the spool, reducing its ribbon capacity.
4) Many spool/spindle combinations have a friction mount and can therefore suffer from rotational slippage.
5) Conventional spools and spindles do not have angled surfaces to guide the insertion process. This makes it more difficult to install a new ribbon on the printer, since the spool must be accurately aligned with the spindle by hand before insertion, and this alignment is often "blind" because the spool obscures the operator's view of the spindle.
6) Longitudinal slippage during printing is not prevented. This is typically corrected by making the ribbon wider than the printed area, thereby unnecessarily wasting ribbon material and increasing its cost.
7) No automatic locking system informs the operator when the spool is entirely inserted onto the spindle, increasing the chance of improper mounting.
8) Finger pressure exerted by the operator for insertion or removal is not moderated.
9) Spools with inner cylindrical surfaces can easily be inserted onto incorrect spindles. This permits undetected use of the wrong spool, resulting in improper operation and possible damage.
What is needed is a spindle/spool design that permits a spool to be inserted on a spindle with minimal rotation of the spool for alignment purposes, that provides effective locking to prevent longitudinal and rotational slippage, that prevents incorrect installation of the correct spools and installation of incorrect spools, and that permits quick and easy insertion/removal of the spool by an untrained operator by correcting for misalignment during the insertion process.